Difluorobenzenes revisited: an experimental and theoretical study of spin–spin coupling constants for 1,2‐, 1,3‐, and 1,4‐difluorobenzene

Abstract

The experimental spin-spin coupling constants (SSCCs) for 1,3- and 1,4-difluorobenzene have been determined anew, and found to be consistent with previously determined values. SSCCs for 1,2-, 1,3-, and 1,4-difluorobenzene have been analyzed by comparing them with the coupling constants computed using the second-order polarization propagator approximation (SOPPA) and the equation-of-motion coupled cluster singles and doubles method (EOM-CCSD). Eighty experimental values have been analyzed using SOPPA calculations, and a subset of 40 values using both SOPPA and EOM-CCSD approaches. One-bond coupling constants (1)J(C-C) and (1)J(C-F) are better described by EOM-CCSD, whereas one-bond (1)J(C-H) values are better described by SOPPA. An empirical equation is presented which allows for the prediction of unknown coupling constants from computed SOPPA values. A similar approach may prove useful for predicting coupling constants in larger systems.

A SOPPA theoretical study of the spin–spin coupling constants of all fluorobenzenes C6HnF6−n (n=0–5)

“…Note, however, that all reported values are very similar. For instance, we have re-determined the SSCC of 1,3-and 1,4-difluorobenzenes obtaining almost identical values as those reported previously [3]. Several other sources have been used to build up Table 1 [4][5][6][7][8][9].…”

Analysis of CF···FC Interactions on Cyclohexane and Naphthalene Frameworks

“…The experimental 4 J FF values are 59.0 Hz and of 6.5 Hz for 3 and 1,3-difluorobenzene, 35 respectively, the latter being the parent molecule of 5. This large difference of more than 50 Hz is clearly related to the "through space" CFFC interaction in 3.…”

“…The J FF value in 1,2-difluorobenzene, the parent molecule of 4, is even more disparate from that in 3 (ca. -21 Hz), 35 but this is a three-bond coupling, which may follow a different through-bond mechanism. Del Bene et.…”

Novel fluoro-substituted benzo- and benzothieno fused pyrano[2,3-c]pyrazol-4(1H)-ones

“…Compounds 8-13 feature a di-or trifluoro substituted benzene ring. Here the 19 F chemical shifts agree well with those found in correspondingly substituted di-or trifluorobenzenes, this is also the case for 19 F, 19 F coupling constants [35][36][37]. The unambiguous determination of 19 F, 19 F couplings was facilitated by recording 1 Hdecoupled 19 F spectra, whereas the 19 F, 13 C spin coupling constants could be easily derived from the 1 H-decoupled 13 C NMR spectra.…”